Electrochemical machining apparatus utilizing a mechanically deformable cathode



J. L. BENDER 3,458,424 ELECTROCHEMICAL MACHINING APPARATUS UTILIZING July 29, 1969 A MECHANICALLY DEFORMABLE CATHODE Filed May 15, 1967 5 Sheets-Sheet l Br D uqwew July 29, 1969 J. 1.. BENDER 3,458,424

ELEC'IHOGHEMICAL MACHINING APPARATUS UTILIZING A MEICHANICALLY DEFORMABLE CA'THODE Filed May 15, 1967 a Sheets-Sheet 2 J. L. BENDER July 29, 1969 3,458,424 ELECTROCHEMICAL MACHINING APPARATUS UTILIZING A MECHANICALLY DEFORMABLB CATHODE 5 Sheets-Sheet 3 Filed May 15 1967 United States Patent US. Cl. 204224 7 Claims ABSTRACT OF THE DISCLOSURE This application discloses a cathode for electrolytic demetallizing processes which is mechanically deformable in shape, thus permitting it to be reduced in external size for insertion into otherwise inaccessible spaces within a metallic work piece, so as to make it possible to demetallize regions adjacent such spaces. The cathode of this invention comprises a conductive metal base portion, a group of flexible, resilient, conductive metal leaves extending from the base portion, said leaves defining between them a plurality of narrow, generally radial slots and terminating in a shaping edge which describes a closed curve. The length of the shaping edge can be reduced or increased, as desired, by first pushing the leaves out of the positions they normally occupy and then permitting them to spring back toward those positions. The cathode of this invention is typically an annular disk having radial slots. This application also discloses a process and an apparatus which utilize the cathode of this invention.

BACKGROUND OF THE INVENTION Field of the inventiom-Electrolytic demetallizing is a well-known process involving the removal of metal from an anodic work piece by passing direct current between a work piece and a shaping cathode which are not in physical contact with each other, while passing a stream of liquid electrolyte between them. The nature of the electrolytic demetallizing which takes place depends to a large extent upon the type of cathode used; see, for example, U.S. Patent No. 3,058,895.

Description of the prior art-Normally, the cathodes used in electrolytic demetallizing have an aperture which either expels or takes up the electrolyte that passes between the cathode and the work piece. For this reason, the cathodes of the prior art are generally of moderate or large size, and they are unsuitable for digging or deburring very small grooves in work pieces.

In addition, the cathodes of the prior art are generally inflexible, and cannot be deformed to fit into hard-toreach places such as the inside of a hollow cylinder.

Advantages of the invention The cathode of this invention is generally made of flexible, resilient sheet metal, e.g., copper, brass, silver, or the like, which is physically deformable, permitting the insertion of the electrode into places which are diflicult to reach.

The shape of the cathode of this invention can also be changed by deformation during the electrolytic demetallization process, resulting in unique effects on the work piece which cannot be obtained with a rigid cathode.

The cathode of this invention is particularly suitable for cutting narrow grooves in conductive metal work pieces, or for deburring the interiors of grooves which have been previously cut.

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Summary of the invention This application relates to a cathode for electrolytic demetallizing apparatus comprising a conductive metal base portion, a group of flexible, resilient, conductive metal leaves extending from said base portion, said leaves defining between them a plurality of narrow, generally radial slots and terminating in a shaping edge which describes a closed curve, said edge being free of electrically insulating material, and said leaves being deformable to vary the length of the shaping edge. This application also relates to a process and apparatus utilizing the above cathode.

The cathode of this invention is commonly an annular disk with radial slots. However, the shaping edge of the cathode of this invention may describe any closed curve such as an ellipse, a semicircle (e.g., the shape of the letter D), or an irregular asymmetrical closed curve.

The radial slots in the cathode of this invention commonly run from the outer edge of the cathode toward but short of the inner edge of a central aperture. However, the slots may, if desired, begin at the inner edge and extend toward the outer edge of the cathode.

The drawings In the drawings:

FIGURE 1 is a top view of one embodiment of the rflisk cathode of this invention shown in its original flat orm.

FIGURE 1a is a fragmentary top view of the same embodiment which has been deformed into the shape of a truncated cone.

FIGURE 2 is a perspective view of the disk-cathode of FIGURE la.

FIGURE 3 is an enlarged fragmentary side elevational view of a portion of the outer, shaping edge of the diskcathode.

FIGURE 4 is a side view partly in elevation and partly in section of an apparatus utilizing the embodiment of the disk-cathode of this invention that is shown in FIG- URES 1 through 3 for removing burrs from an annular internal groove in a sleeve gear which has generally axial gear teeth intersecting the groove, the apparatus being shown in the closed or operating position.

FIGURE '5 is a fragmentary, sectional side view of the same apparatus in the open position in which the disk-cathode can be inserted into or removed from the interior of the cylindrical work pieces.

FIGURE 6 is a magnified view of the vicinity of groove 12 of FIGURE 4.

FIGURE 7 is a fragmentary perspective view of a sleeve gear which can be machined by the practice of this invention.

FIGURE 8 is a top view of another embodiment of the cathode of this invention.

Description of specific embodiments Referring first to FIGURE 1, a sheet metal disk 10 (e.g., copper, brass, silver or the like) has a group of outwardly extending leaves 10L, which define a plurality of slots 10S, extending radially inwardly from the circumference of the disk. The slots terminate at a distance from central aperture 10A, so as not to continue into base portion 10B, from which the leaves extend. The disk is coated on the outer circumferential portions of its two major faces with an electrically insulating material 10C such as an epoxy resin or an insulating paint, leaving edge 10E exposed as shown in FIGURE 3.

FIGURES 1a and 2 show the metal disk 10 deformed into a shape approximating that of a truncated cone, for

use in the apparatus of this invention in a manner to be described below.

Referring now to FIGURES 4, 5, 6 and 7 of the drawings, the invention disclosed herein, including the illustrative embodiment of the cathode which is shown in FIGURES 1 through 3, is described in relation to a problem of deburring an internal corner region of a groove which has been milled or otherwise formed'in a work piece. For purposes of disclosure, the work piece is represented as a sleeve gear 11 having a set of internal gear teeth 11T spaced apart by root channels 11C which lead in a slanting but generally axial direction along the inner wall of the gear.

In the fabrication of the work piece shown, subsequent to the forming of the gear teeth 11T, an internal annular-groove 12 is milled at one end of the sleeve gear ultimately to receive a lock ring (not shown). During the milling operation, burrs are formed, as indicated at B in FIGURE 7, at the regions where the lock ring groove 12 intersects with the root channels 11C, because of the broaching action of the milling tool as it moves from the gear tooth region to the root channel region. These burrs interrupt the desired fiat and smooth annular groove face 12F (FIGURE 6), and thus interfere with proper seating of the lock ring. The present invention provides an electrochemical machining technique for eliminating such burrs.

In FIGURE 6, the above described disk-cathode for an electrolytic demetallizing apparatus is shown projected into the groove 12, with its extreme edge 10E extending towards the internal groove corner region 13 where burrs are to be removed. Thus a gap is defined between the edge face 10E of the cathode and the internal groovecorner of the work piece, and the edge 10E acts to shape the internal groove corner through electrochemical machining.

Electrolyte is shown following a travel path indicated at 14 in FIGURE 6 to enter radially along the bottom wall face 12F of the groove and then flow transversely of the gap. The current flow path through the electrolyte for the disclosed arrangement is generally transverse to the flow of the electrolyte stream. After the stream reaches the burr area at the internal corner region 13 of the groove 12, it exits downwardly through the root channels 12C. As is described in more detail hereinafter, the sleeve gear is mounted upon a pilot element 15 which has a maximum outside diameter slightly less than the root diameter of the gear teeth channels 12C so that the bottom of each channel presents a narrow flow space that exits at the region indicated at 16 in FIGURE 6.

As already stated above, an illustrative embodiment of the cathode 10 for deburring along the internal corner of the groove 12 in the sleeve gear 11 is shown in the form of a disk stamped from sheet metal such as copper, brass, silver or the like. As initially formed, the disk is flat, as pictured in FIGURES 1 and 3, and is provided with a plurality of slots 108 shown extending radially in- .wardly from the outer peripheral or shaping edge 10E,

to terminate in spaced relation from the inner peripheral edge which defines a central aperture 10A for mounting of the disk. Thus, the disk is subdivided into a plurality of integrally connected sector-shaped leaves 10L which permit the disk to be resiliently deformed from the flat contour of FIGURE 1 to a conical contour as illustrated in FIGURE 2.

In particular, in order to insert the disk cathode 10 in the sleeve gear 11, it is first distorted to a more sharply defined conical contour as illustrated in phantom lines in FIGURE 6 and in full lines in FIGURES 1a and 5, in which condition both the width of the radial slots 10S and the length of the shaping edge 10E are reduced. The purpose of this distortion is to effect sufficient contraction of the outer peripheral shaping edge 10E to an effective diameter D (FIGURE In) less than that existing at the crests of the teeth at the milled end of the sleeve gear. With the distorted disk cathode in registry with the groove 12,.its resilient action is allowed to move the disk back towards its initial flat shape (illustrated in phantom at D in FIGURE la) so as to expand its outer peripheral edge to the intermediate conical relationship illustrated in FIGURES 4 and 6. In the latter two figures, the shaping edge 10E of the disk projects into the groove 12 and is directed towards the interior corner regions thereof which'are to be deburred.

A mechanism for mounting of the sleeve gear and for controlling contraction, insertion and subsequent expansion of the disk cathode is shown in FIGURES 4, 5 and 6. The mechanism shown includes a lower support plate 17 mounting a set of upstanding support rods 18 that carry a tool plate 19 in which the mounting ring 15 is secured. The mounting ring 15 is mated with the milled end of the sleeve gear 11 to serve as a pilot post for accurately locating the sleeve gear in the machining apparatus. As indicated previously, the pilot post thus provided has its main diameter slightly undersized relative to the root diameter of the sleeve gear to present an escape passage for the electrolyte.

A vertical guide post 20 has its lower end fixed to the lower support plate 17 and projects through the tool plate 19 and mounting ring 15 to terminate in a stepped diameter upper end 20E which presents an annular seat that carries an inverted cup-shaped shield 21 in position to receive the sleeve gear 11. Another section of the support structure, upper support plate 22 as shown at the top of FIGURE 4, carries a pneumatic piston and cylinder mechanism 23 which includes a depending piston rod 23R that carries a cover plate 24. Piston rod 23R shifts the cover plate 24 between the raised open position of FIGURE 5 and the lowered operating position of FIGURE 4, where in it abuts against the end of the sleeve gear to prevent splashing of electrolyte through the upper end of the gear.

The mechanism for controlling the mechanical shape of the disk cathode 10 includes a sleeve 25 shiftably mounted in telescoping relation upon the guide post 20 and having its lower end fixed to a bracket 26 which is vertically shiftable under the control of a pneumatic piston and cylinder mechanism 27. The piston and cylinder mechanism 27 includes a piston rod 27R that carries the bracket 26. In addition, the lower support plate 17 is provided with an upstanding abutment stop 28 engageable with the bracket 26 to limit downward travel of the sleeve 25. In this lower limit position, as illustrated in FIGURE 4, the upper end of the sleeve 25 terminates in spaced relation from the shield 24.

The sleeve 25 has an annular beveled shoulder 25S adjacent its upper end to serve as a mounting seat for the disk cathode. A floating backing structure of concave conical shape is positioned within the shield 24 in the space above the cathode 10. This floating backing structure includes a common mounting ring 29 and a conical former 30 which presents a generall conical lower face approximating the general contour of the disk cathode 10.

In the operation of the machining apparatus, the sleeve gear 11 is received, as shown in FIGURE 5,.when the cover plate 24 is held elevated by the piston and cylinder mechanism 23 and when the operating sleeve 25 is held upwardly against the shield 21. In this position, the disk cathode is at its maximum conical contour, to cause its circumference to contract sufiicien-tly to fit within the sleeve gear.

In the circumferentially contracted position of FIG- URE 5, the beveled shoulder 25S engages the disk adjacent its inner periphery and the end of the shield 21 cooperatively engages the disk adjacent its outer periphery to determine its shape, with the floating backing structure 29 and 30 at this time being spaced slightly from the main body of the disk. After the sleeve gear is applied and seated on the pilot post 15, the cover plate 24 is lowered into place and the sleeve 25 is lowered to allow expansion of the cathode disk by virtue of its tendency to return to its normal flat position. The outer edge E of the cathode disk, thus, has entered the groove 12 by undergoing a movement which is essentially in the direction in which such edge faces, the edge then being located in obliquely directed relation facing towards the interior corner region 13 of the groove 12. In this position of the parts, the bottom of shield 21 and conical former 30 abut directly against the body of the disk to brace it against pressure effects of the electrolyte introducedthrough a nipple 31 mounted in the pilot ring and projecting downwardly through the tool plate 19.

Normally, the electrolyte fills the cavity between the pilot ring 15 and the cathode disk 10, and it continuously flows outwardly beneath the lower edge of the disk and then transversely of the direction of the gap. The electrolyte flows partly vertically and partly circumferentially in its travel across the gap. Ultimately, as the electrolyte reaches the root channels of the sleeve gear, it exits downwardly between the pilot post and the lower end of the gear.

To energize the electrolytic demetallizing apparatus, a source of DC. voltage (not shown) has its positive side conncted to a contact terminal 32 which is shown in electrical contact with the sleeve gear 11, with the negative side of the voltage source being grounded. Therefore, D.C. current flow passes between the electrode 32 and ground G (here shown connected to the sleeve via the sleeve gear 11 (which acts as the anode), the cathode 10 and finally the sleeve 25. The current path through the electrolyte is seen to be transverse to the direction of the electrolyte flow. Since the current flow generally is strongest at regions where the path across the electrolyte gap is shortest, the electrolytic demetallizing action is believed to be strongest at the approximate internal corner region 13. Thus burrs or other irregularities along this corner region, and particularly at the intersection of the root channels with the groove 12, are rapidly removed, while the groove face 12F against which the lock ring is to seat is maintained substantially flat.

As already mentioned above, in the particular embodiment illustrated herein, the disk cathode 10 has an electrically insulating coating 100 such as an epoxy resin or an insulating paint provided along marginal regions of its lower face (FIGURE 6). This insulation precludes fringing paths for travel of current through the electrolyte, except as such current may emanate from the edge face 10E and the top of the cathode. For the arrangement illustrated, the external coating 10C on the lower face is of particular importance for protecting the flatness of the immediately adjacent groove face 12F. Optimum flatness of this face is maintained in the disclosed arrangement where the angle a (FIGURE 6) measured between a radius of the disk cathode 10 and a line parallel with the axis of the work piece is from about 60 to about 70 and, more particularly, this angle a is set at 65.

While the deburring operation is illustrated with an electrolyte travel path wherein the electrolyte travels radially outwardly from beneath the lower face of the cathode 10, it is also contemplated to employ an electrolyte travel path wherein the electrolyte travels radially outwardly across the upper face of the cathode and then into the corner 13 and out the bottoms of the root channels 11C. Alternatively, electrolyte can be introduced on the upper face of the cathode 10 to travel into the corner and then to exit through the space underlying the cathode.

Any liquid electrolyte can be used in this invention, although water solutions of ionic salts are preferred. Water solutions of the alkali metal nitrate salts such as sodium nitrate or potassium nitrate are particularly preferred, since they cause metal to be removed from an anode only at a slow rate except when the electrolyte is passing across the anode at a high velocity. The use, therefore, of aqueous nitrate salt solutions as the electrolyte in this invention causes the electrolytic demetallizing to take place at a preferentially high rate in the vicinity of corner region 13 (FIGURE 6), due to the fact that the volume of electrolyte flow is constricted in the region of the gap between shaping edge 10B and the work piece, thus increasing the velocity of the flow, while the rate of demetallizing at remote regions of groove 12 and elsewhere is low.

Another desirable electrolyte can be made from the ionic chlorate salts, such as sodium chlorate. Other electrolytes can be made from common salt, calcium chloride, sodium acetate or ammonium sulfate.

It is generally preferred in most embodiments of this invention for the circumference of the cathode to be as close as is practically possible to the surface of the work piece without actually touching, e.g., about 10 to 40 thousandths of an inch, although this requirement is not absolutely critical. The pressure of the electrolyte which is pumped into the apparatus of this invention is preferably from 1 to 10 p.s.i., and the electric current passing from the work piece to the cathode is preferably maintained at from 20 to 150 amps.

The time required to deburr an individual work piece varies with each specific situation, but it rarely exceeds one hour under commercially acceptable conditions. Under normal conditions, when the apparatus described above is operated with an electrolyte pressure of 8 p.s.i. and a current of amps, the deburring process for an annular groove located in the inside surface of a hollow cylindrical body approximately 6 inches in internal diameter is usually complete in about 10 minutes, using an electrolyte consisting of a 10 weight percent water solution of potassium nitrate.

If desired, sleeve 25, disk cathode 10, and the other attached parts 29 and 30 can be rotated during operation of the apparatus, to insure uniform demetallization of groove 12. Or, in the alternative, work piece 11 and cover plate 24 can be rotated while the other elements are kept stationary. In the latter case, contact terminal 32 should be of brush or braid construction, to provide reliable contact between the anode and the work piece 11. When the disk cathode and the work piece rotate with respect to each other in either manner just described, the leaves 10L of the disk cathode should desirably be relatively narrow, in order to reduce the slowdown in electrolytic action which tends to take place because of the lack of exact parallelism between the outer edge of each individual leaf and the local portion of the wall of the groove that is being demetallized at any given moment by that particular advancing leaf.

If the disk cathode and the work piece do not rotate with respect to each other, the shaping edge of the slotted cathode may be, if desired, some form other than circular, as for example an ellipse.

For the particular arrangement disclosed herein, the cathode 10 and the sleeve 25 are of a conductive metal, while the shield 21, the backing structure 30, the pilot post 15 and the cover plate 24 are of an insulating or non-conductive material such as a glass-filled molded epoxy resin. This arrangement isolates the conductive paths which are possible through the electrolyte to the particular area where demetallizing is desired.

The invention is applicable to other operations requiring machining at a remote location, such as the internal corner of a groove. For example, where the groove is located on the outer periphery of a work piece, rather than on the inner periphery as described in relation to the sleeve gear 11 of this disclosure, a conductive sheet metal disk cathode 40, such as shown in FIGURE 8, can be employed. The cathode 40 defines an aperture 40A at its center and has slots 40S extending radially outward from the center aperture to terminate in spaced relation from the outer periphery of the disk. The slots 408 are defined by integrally connected sector-shaped leaves 40L, which extend radially inward toward the center aperture from the base portion 40B at the outer periphery of the disk.

For this type of cathode, a different deforming apparatus will be employed normally to hold the disk in a maximum conical relationship to enable its insertion around the work piece. Thereafter, the disks inner peripheral edge face is projected into the exterior groove on the work piece (not shown) for etfecting electrolytic demetallizing. A coating of electrically insulating material 40C is shown on the upper marginal face of the disk to provide control of the current, path. When the disk cathode 40 is aligned with the groove, it is allowed to return towards its initially fiat shape to eflect shrinkage of its inner peripheral edge to cause the same to enter into the work piece groove.

While the invention is shown and described in connection with the application of disk cathodes to cylindrical work pieces, the invention also contemplates the use of cathodes of other edge contour such as straight edged cathodes to be positioned in corresponding relation to the interior of straight grooves. The localized groove finishing action associated with the placement and angle of attack of the cathode edge in the embodiment shown is contemplated for other final machining or deburring operations with appropriate modifications-of the apparatus used.

The above detailed description of this invention has been given for clarity of understanding only. No unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. Apparatus for removing metal from an elongated notch in a conductive metal part, said apparatus comprising (1) a conductive sheet metal cathode presenting a conductive edge for entry into said notch, -(2) means for relatively moving said part and said cathode to locate said edge adjacent to and facing said notch, (3) means for changing the mechanical shape of said cathode while said edge is adjacent said notch to project said edge into said notch toward the walls defining an interior corner region of said notch to define a gap therebetween, (4) means for directing electrolyte into said notch to span said gap between said edge and said walls with a stream of electrolyte, and (5) means for connecting a source of D.C. voltage across said part and said cathode in a sense to make said conductive metal part anodic.

2. The apparatus of claim 1 wherein said sheet metal cathode comprises: a conductive metal base portion, a group of flexible, resilient conductive metal leaves extending from said base portion, said leaves defining between them a plurality of narrow, generally radial slots and terminating in a shaping edge which describes a closed curve, said edge being free of electrically insulating material, said leaves being deformable, in response to said means for changing the mechanical shape of the cathode, to vary the width of said radial slots and the length of said shaping edge.

3. The apparatus of claim 2 in which at least one of the opposite major faces of each of said leaves carries, adjacent said shaping edge, a layer of electrically insulating material.

4. The apparatus of claim 2 in which said sheet metal cathode is formed of a conductive metal annular plate the outer edge portion of which is said base portion, from which base portion said group of metal leaves extends inwardly to terminate at a central aperture, the inner edges of said leaves around said aperture forming the shaping edge whose length may be varied by deformation of the leaves.

5. A device for removing metal from an annular region on the inside of a hollow metal cylinder, said device comprising (1) a conductive metal disk-cathode having a plurality of slots extending from the circumference toward the center of said disk, the length of said slots being less than the radius of said disk, said disk further defining an aperture at its center which is separate from said slots, whereby said disk is symmetrically deformable to vary the circumference of said disk, there extending through said aperture a conductive metal bar in a direction axial of said disk, at least one face of said disk carrying, about its entire circumference, a layer of electrically insulating material, the circumferential edge of said disk being free of electrically insulating material so as to be cathodically active; (2) means for relatively positioning the conductive metal cylinder and the diskcathode so that the entire circumferential edge of said disk-cathode is adjacent to but not in contact with the annular region of said cylinder from which metal is to be removed; (3) means for subjecting the gap between said disk-cathode and said annular region to a continuous flow of liquid electrolyte, and (4) means for connecting a source of D.C. voltage across said metal cylinder and said disk-cathode in a sense to make said metal cylinder anodic.

6. The device of claim 5 in which said means for relatively positioning the conductive metal cylinder and the disk-cathode include means for deforming said disk into approximately a truncated cone while it is being inserted into or removed from said cylinder, and means for at least partly releasing said disk from its said deformation while it is in place in said cylinder whereby the periphery of said disk expands into close relationship to said annular region.

7. The device of claim 5 in which said disk-cathode and said hollow metal cylinder are rotatable with respect to each other about the axis of said cylinder.

References Cited UNITED STATES PATENTS 2,367,909 1/1945 Wanner 204-297 FOREIGN PATENTS 197,170 4/1922 Great Britain.

JOHN H. MACK, Primary Examiner SIDNEY S. KANTER, Assistant Examiner US. Cl. X.R. 204143, 289

Dedication 3,458,424.J0seph L. Bender, Wheeling, I11. ELECTROCHEMICAL MA- CHINING APPARATUS UTILIZING A MECHANICALLY DE- FORMABLE CATHODE. Patent dated July 29, 1969. Dedication filed Dec. 23, 1971, by the assignee, Anocut Engineering Company. Hereby dedicates to the Public the portion of the term of the patent subsequent to Dec. 24, 1971.

[Oyficz'al Gazette December 5, 1972.] 

